Adjustable blank firing attachment for automatic firearms



June 16, 1964 E. M. HARVEY 3,137,204

ADJUSTABLE BLANK F'IRING ATTACHMENT FOR AUTOMATIC FIREARMS Filed May 14, 196s arent SLZM Patented .lune i6, i964 ice 3,137,204 ADJUSTABLE BLANK FiRiNG ATTACEEMENT FR AUTMATIC FIREARMS Earle M. Harvey, Agawam, Mass., assigner to the United States of America as represented by the Secretary of the Army Filed May 14, 1963, Ser. No. 280,473

4 Claims. (Cl. 89--14 (Granted under Title 35, US. Code (1952), sec. 266) The invention described herein may be manufactured and used by or for the Government for governmental purposes without the payment to me of any royalty thereon.

Tlu's invention relates to blank firing attachments for automatic rearms and is more particularly directed to an attachment which can be readily adjusted to vary the gas pressure imparted to the recoiling parts of the rearm.

In order to permit the utilization of blank ammunition for the training of military personnel in the handling and operation of automatic irearms, the muzzle end of the barrel is generally fitted with an attachment having a fixed orifice for restricting the forward iiow of the propellant gases to provide sufficient pressure to function the recoiling parts of the firearm. While these blank firing attachments produce the required automatic operation of the firearm, the orifice must be designed so that the pressure of the propellant gases will be considerably greater than the energy required to function the recoiling parts.

In many firearms the excessive recoil forces produced by conventional blank ring attachments are readily absorbed by the recoiling parts of the firearm. However, in some iiirearms, the energy imparted to the recoiling parts must be maintained within a relatively narrow range. For example, in the Cal. 7.62 mm. M73 Machine Gun, insufficient recoil movement of the bolt will result in a failure to eject the tired cartridge case while excessive recoil velocity of the bolt will prevent the critical transfer of the iired case to a pivotal gripper member for subsequent ejection through the bottom of the firearm receiver. Consequently, considerable diiculty has been experienced in selecting the proper orifice size to be employed in the blank tiring attachment.

This problem is even further complicated by the fact that the peak pressure produced by blank ammunition normally varies from one production lot to another. In addition, any prolonged or unusually severe operation of the firearm serves to vary the energy requirements of the recoiling parts. Another factor responsible for variations in the gas pressures provided by blank firing attachments is the tolerances permitted in the dimensions of the attachment itself. Also, the manner in which the iirearm is mounted plays an important role in determining the power requirements of the recoiling parts. As a result, previous attempts to selectively iit a blank firing attachment of the particular power requirements of the M73 firearm have required considerable testing with a plurality of attachments.

Accordingly, it is a basic object of this invention to provide a simple, rugged, and compact blank firing attachment which can be readily adjusted to yield the optimum recoil energy required by the particular firearm on which the attachment is mounted.

A more specific object of the present invention is to provide an adjustable blank tiring attachment in which the orifice for the passage of the propellant gases may be readily increased or decreased in size without the necessity for any replacement of parts or removal of the attachment from the firearm.

It has been found that these objects may be advantageously accomplished by providing a blank tiring attachment with a rotatable transverse pin having an eccentn'cally formed groove of predetermined contour disposed in the path of the propellant gases issuing from the muzzle end of the firearm barrel. One end of the pin is suitably slotted to permit an index mark thereon to be rotated and locked into alignment with a plurality of graduations which are consecutively numbered to correspond with the size of the cross-sectional area disposed in the path of the escaping gases at any angular position of the eccentric groove.

The specific nature of the invention as well as other objects and advantages thereof will clearly appear from a description of a preferred embodiment as shown in the accompanying drawings in which:

FIG. 1 is a longitudinal section through the muzzle end of an automatic firearm provided with the blank firing attachment of the present invention adjusted for maximum passage of the recoil gases;

FIG. 2 is a right side view of the attachment showing the adjusting screw rotated to the upper limit of the calibrated scale;

FIG. 3 is a cross-sectional view taken along line 3-3 of FIG. l to show the transverse conguration of the adjusting screw;

FIG. 4 is a fragmentary view similar to FIG. l but showing the adjusting screw positioned for minimum gas passage;

FIG. 5 is a side view similar to FIG. 2 but showing the adjusting screw in the minimum position to FIG. 4; and

FIG. 6 is a sectional view taken along line 6-5 in FIG. 5 to show the transverse configuration of the locking means for the adjusting screw.

As shown in the figures, the blank firing attachment of this invention comprises a generally rectangular block l2 adapted to be threaded as shown at 14 to the front end of a bearing 15 surrounding the muzzle end of a longitudinally slidable barrel 16. Immediately forwardly of threads 14, the interior of block l2 is formed with an annular stop shoulder 18 designed to contact the front end of bearing 15 which is in turn secured to a sleeve 17 suitably fixed in the front end of a barrel jacket 19.

Extending forwardly of stop shoulder 18 is a conical well 2t) terminating in a forwardly opening orice 22 in longitudinal alignment with the bore axis of barrel 14. Orilice 22 is partially intersected by a hole 24 which extends transversely through block l2 to terminate in an enlarged recess 26 formed in one side of block l2 by the intersection of a circular portion 28 and the open end of a U-shaped section 30.

Transverse hole 24 serves to rotatably seat a pin 32 having an enlarged cylindrical head 34 engageable in circular portion 28. The underside of 'head 34 is annularly beveled, as indicated at 36, to mate with a correspondingly shaped seat 3S provided in the floor of circular portion 28 and of sufficient depth to position the top of head 34 into flush alignment with the outer wall surface of block 12. Thus, a radially extending index arrow 40 inscribed on the top of head 3d can be accurately aligned with each of a series of graduation marks 42 radially disposed about substantially half of the circumference of circular portion 28. The desired alignment is achieved by rotating pin 32 in the proper direction and head 34 is, therefore, suitably slotted, as indicated at 44, in FIG. 2 to receive the blade end of a screwdriver or other similar tool.

The body of pin 32 is formed with a substantially central bearing surface 45 which is grooved, as shown at 46, to provide an eccentric surface 48 of progressively increasing depth. The required eccentric contour may be edectively obtained by a series of adjacent angular cuts which will provide a plurality of fiat surfaces disposed at progressively increasing depths relative to the exterior periphery of pin 32. Or, if preferred, surface 48 may be helically formed to provide a contour which will not be with the corresponding wallsof orilice 22.

interrupted byV the ridges formed at the intersection'of surfaces f different angularity. -Groove 46 is so located along the axis ofpin 32 and is of such width that, when the'latter is properly seated in block l2, the oppositey i walls of groove 46 Vare positioned in tangential alignment A bolt 521s threadably mounted `in block l2 through thecenter of U-shaped section 30 along'an axis substantially parallel to that of pinV 32 and is provided withV an enlarged head 54 adapted to overlie` a stepped surface 50 extending circumferentially` along slightly Ymore than half v of theperipheralredge of head 34 on pin 32.V A pair of crossedi slots 56 on bolt head 54-provide access for a suitable tool ,by means of which bolt 52 maybe rotated into and out ofrlocking engagement withsurface 56 on adjusting pin 32.V The terminal ends of stepped-.surface 50c-ire 4 Although a particular embodiment ofthe invention has been described in detail herein, it is evident that many variations may be devised witlriintheV spirit andyscope thereof and the following claims are rintended to include such variations. Y

claim: A L l. blankiringjattachrnent for a recoil operated tire-y arm having a reciprocatingbarrcL said attachmentV corn-v prising a block Vhaving an axialV orifice Vtherethroughfori Vthe passagey of the discharge gases producedv bythe iiiring i of a blank cartridge, means forq securing saidattachment to therearm in axial alignment with the muzzle end of the barrel, means for adjusting the size of said oriiiceito arcuatelyiormed, as shownv at', to cooperate with'the 'Y circular periphery of locking 'bolt 152 for limitingthe rotation of adjusting pinhead 34 between minimum'and maximum gas passage positions of` eccentricgroove 46. In addition, index arrow' iti islocated on head'd Vto align with Vthe corresponding graduation mark .42 at the beginning or end of the calibratedscale wheneverv adjusting pin 32 is in one of these limiting positions.V Y

Thus, whenV it is desired to utilize an automatic rearm threaded onto the muzzle end of the barrel, orthe bearing in the particular firearm depicted in the drawings, and

adjusting pin 32 rotated until -index arrow iti-thereon isv aligned substantially midway of graduation marks 42 and locked in such position by tightening bolt 52. Whena blank cartridge is subsequently fired, the forward ov/ of i v for training purposes, the blank ring attachment'is lsimply the propellant gases Will be partially blocked bythe wallsYV of conical Well 20 las well as by eccentric groove 46 in-V adjusting pin 32.` This restricted gas flow will,y ofcourse, Vincrease the gas pressure in the firearm `and provideV the necessary recoil of the moving parts.A

However, if such pressure vis too low or'too high,as

evidenced by the particular action of the yrecoiling parts, bolt 52 is loosened'and adjusting pinV 32 rotated Yin the direction and to the extent estimated to yield the proper firearm operation and locked 1in such position. Another blank cartridge is fired and the lforegoing adjustment Y repeated until'the moving parts are deemed to recoilr in the samev manner and at the same velocityas would bev the case if live ammunition were used. Y

Thus, there is here provided a blank tiring attachment which can be quickly and easily adjusted to provide optimum firearm operation without the necessity Vfor Vre-V y moving the attachment or any of the parts thereof from l the rearm. Consequently, the rearm may continue to;

be utilized for training purposes regardless of any undue Y variation in the power Vcharacteristics of the ammunition or any change in the energy required to recoil the moving parts. Furthermore, the use of an eccentric surface for blocking the forward ow of the propellantA gases permits' the blank yfiring attachment to be adjusted in extremely small increments and over a vrelatively wide range.

control the flow of` gases therethrough andthereby provide suiiicient pressureagainst the muzzle end Vof therbarrelto simulate Vthe action normally impacted tothe recoiling parts bylive'amrnunitiomand means for locking said'g'as control meansjin any of a plurality of adjusted positionsgl'f V2.'lhe combination delin'ed in claim V1 Whereinsaid means for adjustably controlling theow ofgases through said orifice in said blank-tiring attachmentcomprisesa rotatable pin transversely mounted. in said `block to parr ytially intersect said oriice at substantially yright angles i thereto, said pin having Va groove kof progressively increasing depth and disposed in intersectingalignment with said orilice. Y"

3. A blank Vfiring attachment for a recoil. operated fire,- arm having a reciprocating. barrel, said attachmentcomprising a block having a conical well communicating with a forwardly disposed'axial orifice for the passage of the selectiveV alignment with said index arrow, said transverse pin having an eccentric groove YVtherein yof progressively increasing depth disposed iny intersecting alignment with said axial orifice, a ,stepr surface peripherallyformedfin said enlarged head and',l radially orientedrrelativeV t0 said' Y eccentric groove to align said index arrow vwith said gra- Y Y duations in direct accordance withthe extent of restriction 1 of saidy axial orifice, and means for lockingrsaid adjusting Y. i Y pin in anyV of a pluralityof rotated positions. f

4. The combinationidened inrclaim 3 ,wherein said` means forY locking said adjusting VVpin 'comprises a bolt Y, f threadably secured in said block with aheaddisposed toV f engagev said step surface on said enlarged head ofV said adjusting'pin and prevent rotation thereof.

References Cited in the tile of this patent Y UNITED STATES lPATENTS 2,330,210 Garage sept. 2s; 1943 

1. A BLANK FIRING ATTACHMENT FOR A RECOIL OPERATED FIREARM HAVING A RECIPROCATING BARREL, SAID ATTACHMENT COMPRISING A BLOCK HAVING AN AXIAL ORIFICE THERETHROUGH FOR THE PASSAGE OF THE DISCHARGE GASES PRODUCED BY THE FIRING OF A BLANK CARTRIDGE, MEANS FOR SECURING SAID ATTACHMENT TO THE FIREARM IN AXIAL ALIGNMENT WITH THE MUZZLE END OF THE BARREL, MEANS FOR ADJUSTING THE SIZE OF SAID ORIFICE TO CONTROL THE FLOW OF GASES THERETHROUGH AND THEREBY PROVIDE SUFFICIENT PRESSURE AGAINS THE MUZZLE END OF THE BARREL TO SIMULATE THE ACTION NORMALLY IMPACTED TO THE RECOILING PARTS BY LIVE AMMUNITION, AND MEANS FOR LOCKING SAID GAS CONTROL MEANS IN ANY OF A PLURALITY OF ADJUSTED POSITIONS. 